Theoretical systematics in testing the Cosmological Principle with the kinematic quasar dipole

Guandalin, Caroline; Piat, Jade; Clarkson, Chris; Maartens, Roy

doi:10.48550/arxiv.2212.04925

Cited by 7 publications

(7 citation statements)

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“…A more recent study [133] succeeds in recovering the CMB dipole, but larger errors mean that the inferred dipole is consistent within 3σ with observations that claim an excess, such as, for example, [113] 33 . Separately, the Baldwin-Ellis methodology has been questioned [137][138][139]. These points aside, it is worth bearing in mind that these observations, along with [90,91], are serious claims that could potentially upend modern cosmology, but the results are preliminary.…”

Section: Prologuementioning

confidence: 99%

Is the observable Universe consistent with the cosmological principle?

Aluri

Cea

Chingangbam

et al. 2023

Class. Quantum Grav.

108

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The Cosmological Principle (CP) -- the notion that the Universe is spatially isotropic and homogeneous on large scales -- underlies a century of progress in cosmology. It is conventionally formulated through the Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) cosmologies as the spacetime metric, and culminates in the successful and highly predictive $\Lambda$-Cold-Dark-Matter ($\Lambda$CDM) model. Yet, tensions have emerged within the $\Lambda$CDM model, most notably a statistically significant discrepancy in the value of the Hubble constant, $H_0$. Since the notion of cosmic expansion determined by a single parameter is intimately tied to the CP, implications of the $H_0$ tension may extend beyond $\Lambda$CDM to the CP itself. This review surveys current observational hints for deviations from the expectations of the CP, highlighting synergies and disagreements that warrant further study. Setting aside the debate about individual large structures, potential deviations from the CP include variations of cosmological parameters on the sky, discrepancies in the cosmic dipoles, and mysterious alignments in quasar polarizations and galaxy spins. While it is possible that a host of observational systematics are impacting results, it is equally plausible that precision cosmology may have outgrown the FLRW paradigm, an extremely pragmatic but non-fundamental symmetry assumption.

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Section: Prologuementioning

confidence: 99%

Is the observable Universe consistent with the cosmological principle?

Aluri

Cea

Chingangbam

et al. 2023

Class. Quantum Grav.

108

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“…Despite of the simplicity and overall observational consistency of the CP, a few challenges have developed during the past several years which appear to consistently question the validity of the CP on cosmological scales larger than 100M pc and motivate further tests to be imposed on its validity. Some of these challenges pointing to preferred directions on large cosmological scales include the quasar dipole [2][3][4][5][6], the radio galaxy dipole [7][8][9], the bulk velocity flow [10][11][12][13], the dark velocity flow [14], the CMB anomalies [15,16], the galaxy spin alignment [17][18][19], the galaxy cluster anisotropies [20], and a possible SnIa dipole [21,22]. These observational challenges of the CP may be indirectly connected with other tensions of the standard ΛCDM model including the Hubble [23][24][25] and growth ten- * leandros@uoi.gr sions [26][27][28][29] where the best fit parameter values of the model H 0 and σ 8 appear to be inconsistent when probed by different observational data.…”

Section: Introductionmentioning

confidence: 99%

On the homogeneity of SnIa absolute magnitude in the Pantheon+ sample

Perivolaropoulos

Skara

2023

Monthly Notices of the Royal Astronomical Society

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We have analysed the Pantheon+ sample using a new likelihood model that replaces the single SnIa absolute magnitude parameter M used in the standard likelihood model of Brout et. al. (2022) with two absolute magnitude parameters M<, M> and a transition distance dcrit that determines the distance at which M changes from M< to M>. The use of this likelihood dramatically changes the quality of fit to the Pantheon+ sample for a ΛCDM background by Δχ2 = −19.6. The tension between the M< and M> best fit values is at a level more than 3σ with a best fit dcrit very close to 20 Mpc. The origin of this improvement of fit and M< − M> tension is that the new likelihood model, successfully models two signals hidden in the data: 1. The volumetric redshift scatter bias systematic and 2. A mild signal for a change of intrinsic SnIa luminosity at about 20 Mpc. This interpretation of the results is confirmed by truncating the z < 0.01 Hubble diagram data from the Pantheon+ data where the above systematic is dominant and showing that the M< − M> tension decreases from above 3σ to a little less than 2σ. It is also confirmed by performing a Monte Carlo simulation which shows that the maximum significance of the SnIa luminosity transition ($\Sigma \equiv \frac{|M_>-M_<|}{\sqrt{\sigma _{M_>}^2+\sigma _{M_<}^2}}$) in the real data, is larger than the corresponding maximum significance of $94{{\%}}$ of the corresponding homogeneous simulated samples.

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“…In addition to the above theoretical challenges, the two main components in the ΛCDM model, dark matter (DM) and dark energy (DE), are poorly understood. Moreover, there are also some tensions between the cosmological and astrophysical observations and the ΛCDM model, which include the Hubble tension [3,[33][34][35][36][37][38][39][40] (5σ), growth tension [41][42][43] (2-3σ), CMB anisotropy anomalies [22,[44][45][46][47][48][49][50][51][52][53] (2-3σ), cosmic dipoles [23, [54][55][56][57][58][59][60][61][62][63] (2-5σ), Baryon Acoustic Oscillation (BAO) curiosities [64][65][66] (2.5-3σ), parity violating rotation of CMB linear polarization [67][68][69][70], small-scale curiosities [71][72][73][74], age of the universe [75], the Lithium problem [76] (2-4σ),the quasar Hu...…”

Section: Introductionmentioning

confidence: 99%